Seat belt retractor

ABSTRACT

A seat belt retractor including a spool for winding up a seat belt; and a locking mechanism having a locking member that rotates together with the spool in the normal state, but is prevented from rotating in a belt withdrawing direction in the event of an emergency, generating a rotational difference relative to the spool. The spool further including an energy absorbing pin that is disposed on the spool and the locking member to limit the load applied to the seat belt when the rotational difference is generated between the spool and the locking member. The energy absorbing pin has a shaft portion that is fitted in a hole of the spool and a head portion that is in contact with the locking member. The head portion comprises a curved contact surface to be in contact with the locking member.

BACKGROUND

Conventionally, a seat belt apparatus installed in a vehicle, such as an automobile, restrains an occupant with a seat belt in the event of an emergency as mentioned above to prevent the occupant from being thrown from a vehicle seat.

The present application relates to a technical field of a seat belt retractor, for retracting a seat belt such that the seat belt can be freely withdrawn and wound, and, more particularly, relates to a seat belt retractor which comprises an energy absorbing mechanism (“EA mechanism”) and to a seat belt apparatus having the aforementioned seat belt retractor. The EA mechanism is a mechanism which limits load on a seat belt, worn by an occupant, by the action of an energy absorbing member at the time of preventing withdrawal of the seat belt in the event of an emergency such as a collision in which a large deceleration acts on a vehicle, thereby absorbing the energy of the occupant.

Conventionally a seat belt retractor used in an seat belt apparatus includes a torsion bar as an EA mechanism to absorb the occupant's kinetic energy by limiting the load on the seat belt in the event of an emergency when the occupant wears the seat belt. To effectively obtain limited load, various seat belt retractors may provide another EA mechanism that cooperates with the torsion bar to absorb the occupant's kinetic energy.

A seat belt retractor may include a long energy absorbing pin (or an energy absorbing wire) inserted into an axial hole of a spool as an additional EA mechanism. The energy is absorbed drawing the energy absorbing pin with bending deformation thereof in the event of emergency.

There is a need for an inexpensive seat belt retractor which allows an energy absorbing pin to be easily assembled and allows for improved productivity even with obtaining stable limited load and to provide a seat belt apparatus employing the seat belt retractor.

There is also a need for a seat belt retractor which can be made compactly even with such an arrangement that a head portion of an energy absorbing pin tilts and to provide a seat belt apparatus employing the seat belt retractor.

SUMMARY

One embodiment disclosed herein relates to a seat belt retractor comprising a spool for winding up a seat belt; and a locking mechanism having a locking member that rotates together with the spool in the normal state, but is prevented from rotating in a belt withdrawing direction in the event of an emergency, generating a rotational difference relative to the spool. The spool further comprises an energy absorbing pin that is disposed on the spool and the locking member to limit the load applied to the seat belt when the rotational difference is generated between the spool and the locking member. The energy absorbing pin has a shaft portion that is fitted in a hole of the spool and a head portion that is in contact with the locking member. The head portion comprises a curved contact surface to be in contact with the locking member.

Another disclosed embodiment relates to a seat belt apparatus comprising a seat belt retractor for winding up a seat belt; a tongue slidably supported by the seat belt withdrawn from the seat belt retractor; and a buckle to which the tongue can be detachably latched. In the event of an emergency, the seat belt is prevented from being withdrawn by the seat belt retractor so that the seat belt apparatus restrains an occupant.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only, and are not restrictive of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the present invention will become apparent from the following description, appended claims, and the accompanying exemplary embodiments shown in the drawings, which are briefly described below.

FIG. 1 is an illustration schematically showing a part of a seat belt retractor.

FIG. 2( a) is a front view of an example of an energy absorbing pin, FIG. 2( b) is a left side view of the example of FIG. 2( a), FIG. 2( c) is a front view of another example of the energy absorbing pin, FIG. 2( d) is a left side of the example of FIG. 2( d), FIG. 2( e) is a front view of still another example of the energy absorbing pin, and FIG. 2( f) is a left side of the example of FIG. 2( e).

FIG. 3 is a right side view of the locking base in a state that the energy absorbing pin is assembled.

FIGS. 4( a) and 4(b) show the behavior of the energy absorbing pin shown in FIG. 2( a), wherein FIG. 4( a) is an illustration showing the normal state thereof and FIG. 4( b) is an illustration showing the state that the energy absorbing pin is drawn and bent in the event of an emergency.

FIG. 5 is an illustration schematically showing an example of a seat belt apparatus.

FIG. 6( a) is a sectional view schematically showing an example of a seat belt retractor with an energy absorbing pin, FIG. 6( b) is a front view of the energy absorbing pin, and FIG. 6( c) is a left side view of the energy absorbing pin.

FIG. 7( a) is a graph showing limited load in which the overshooting of the energy absorbing pin is prevented, and FIG. 7( b) is a graph showing limited load in which the overshooting of the energy absorbing pin occurs.

FIGS. 8( a)-8(c) show the behavior of the energy absorbing pin, wherein FIG. 8( a) is an illustration showing the normal state thereof, FIG. 8( b) is an illustration showing the initial state of the drawing and bending action of the energy absorbing pin, and FIG. 8( c) is an illustration showing the state in which the energy absorbing pin is drawn and bent in the event of an emergency.

FIGS. 9( a)-9(c) show an energy absorbing pin described in Patent document 1, wherein FIG. 9( a) is a front view thereof, FIG. 9( b) is a left side view thereof, and FIG. 9( c) is an illustration showing the assembled state of the energy absorbing pin.

DETAILED DESCRIPTION

The seat belt retractor of the present disclosure is suitably used as a seat belt retractor which is used in a seat belt apparatus installed in a vehicle such as an automobile and which prevents a seat belt from being withdrawn while absorbing inertial energy of an occupant by limiting the load applied to the seat belt with an energy absorbing member in the event of an emergency such as a vehicle collision.

FIG. 5 is an illustration schematically showing a seat belt apparatus. In the seat belt retractor 3 used in the seat belt apparatus 1, a torsion bar is provided as an EA mechanism to absorb the occupant's kinetic energy by limiting the load on the seat belt in the event of an emergency when the occupant wears the seat belt. To effectively obtain limited load, various seat belt retractors 3 provide another EA mechanism that cooperates with the torsion bar to absorb the occupant's kinetic energy.

The seat belt retractor 3 includes a long energy absorbing pin (or an energy absorbing wire) inserted into an axial hole of a spool as an additional EA mechanism. The energy is absorbed drawing the energy absorbing pin with bending deformation thereof in the event of emergency.

FIG. 6( a) is an illustration schematically showing an example of the seat belt retractor having the energy absorbing pin, FIG. 6( b) is a front view of the energy absorbing pin, and FIG. 6( c) is a left side view of the energy absorbing pin. The locking mechanism 11 comprises a pawl 15, a locking base (corresponding to the locking member of the present invention) 16 which pivotally supports the pawl 15, and a lock gear 17. The locking base 16 is connected to one end side (the right end side in FIG. 6( a)) of the torsion bar 12 such that the locking base 16 can rotate together with the torsion bar 12. The lock gear 17 is supported by the torsion bar 12. In this case, the lock gear 17 normally rotates together with the torsion bar 12 and the locking base 16, but is stopped from rotating at least in the belt withdrawing direction by the operation of the deceleration sensing mechanism 10 in the event of an emergency. By the stoppage of the rotation in the belt withdrawing direction, a rotational difference is generated in the lock gear 17 relative to the torsion bar 12 and the locking base 16. The pivotal movement of the pawl 15 is controlled by a cam hole (not shown) of the lock gear 17 so that the pawl 15 engages with one of internal teeth 18 of the side wall 8 a of the frame 8, thereby preventing the locking base 16 from rotating in the belt withdrawing direction.

The left end side of the torsion bar 12 (a portion on the left end side relative to the middle in the axial direction in FIG. 6( a)) is connected to the spool 9 such that the torsion bar 12 can rotate together with the spool 9. The spool 9 normally rotates together with the torsion bar 12 and the locking base 16 However, in the event of an emergency, the torsion bar 12 rotates relative to the locking base 16 in the belt withdrawing direction as the locking base 16 is stopped from rotating in the belt withdrawing direction by the operation of the deceleration sensing mechanism 10. The spring force of the spring mechanism 13 biases the spool 9 in the belt winding direction via the torsion bar 12.

A long energy absorbing pin 19 is arranged between the spool 9 and the locking base 16. As shown in FIGS. 6( b) and 6(c), the energy absorbing pin 19 comprises a long shaft portion 19 a and a head portion 19 b formed at one end of the shaft portion 19 a. The shaft portion 19 a penetrates the locking base 16 in a direction parallel to the axial direction of the spool 9 and is fitted into an axial hole 9 a of the spool 9. The head portion 19 b is formed to have a rectangular shape as seen from the side and the surface thereof around the shaft portion 19 a functions as a contact surface 19 b 1 which engages with the locking base 16. The contact surface 19 b 1 is a flat surface and the shaft portion 19 a projects vertically from the center of the contact surface 19 b 1.

In the seat belt retractor 3 having the aforementioned structure, when the seat belt is not used, the biasing force of the spring 13 fully winds the seat belt 4. By withdrawing the seat belt 4 at a normal speed for wearing, the spool 9 rotates in the seat belt withdrawing direction so that the seat belt 4 is smoothly withdrawn. After the tongue 6 slidably attached to the seat belt 4 is inserted into and latched with the buckle 7 fixed to the vehicle body, the excessive length of the seat belt 4 is wound onto the spool 9 by the biasing force of the spring 13 so that the seat belt 4 is fitted to the occupant to the extent that the occupant does not feel stress.

As a vehicle deceleration significantly larger than that in the normal state is generated in the event of an emergency, the deceleration sensing mechanism 10 is activated by the large deceleration to stop the rotation of the lock gear 17 in the belt withdrawing direction. Then, the pivotal movement of the pawl 15 is controlled by a cam control hole of the lock gear 17 so that the pawl 15 engages with one of the internal teeth of the side wall 8 a of the frame 8. Since the spool 9 tries to continue to rotate in the belt withdrawing direction while the locking base 16 is stopped from rotating in the belt withdrawing direction, the torsion bar 12 is twisted. After that, the spool 9 rotates in the belt withdrawing direction relative to the locking base 16 while twisting the torsion bar 12. The torsional load on the torsion bar 12 limits the load applied to the seat belt 4 to, in turn, limit the impact exerted on the occupant.

The relative rotation of the spool 9 relative to the locking base 16 draws a portion 19 a 1 of the shaft portion 19 a of the energy absorbing pin 19 from the axial hole 9 a of the spool 9. The portion 19 a 1 of the shaft portion 19 a is bent and deformed in the circumferential direction between the spool 9 and the locking base 16 as it is drawn from the axial hole 9 a. Further, when the energy absorbing pin 19 is subjected to the bending load, the locking base 16 applies force to the contact surface 19 b 1 of the head portion 19 b of the energy absorbing pin 19 so that the head portion 19 b is bent in the circumferential direction about the radial axial line. The drawing and bending load of the energy absorbing pin 19 composed of the bending deforming force of the portion 19 a 1 of the shaft portion 19 a, the friction force between the spool 9 and the portion 19 a 1 of the shaft portion 19 a, and the bending force at the head portion 19 b all may limit the load applied to the seat belt 4.

The kinetic energy is absorbed by the torsional load of the torsion bar 12 and the drawing and bending load (e.g., the bending load and the friction load) of the energy absorbing pin 19. The limited load contribution of the energy absorbing pin 19 ends as the portion 19 a 1 of the shaft portion 19 a of the energy absorbing pin 19 is completely drawn out of the axial hole 9 a, leaving only the torsional load of the torsion bar 12 to absorb the kinetic energy.

In the EA mechanism using the energy absorbing pin 19, during transition in the event of an emergency from the normal state as shown in FIG. 8( a) to the state as shown in FIG. 8( b), the drawing and bending load is rapidly increased at an initial stage of the drawing action in which the energy absorbing pin 19 is drawn out by relative rotation of the spool 9 in the belt withdrawing direction relative to the locking base 16. Accordingly, as shown in FIG. 7( b), the limited load overshoots at the initial stage of the drawing action of the energy absorbing pin 19. After the bending and drawing of the energy absorbing pin 19 becomes in a stationary state as shown in FIG. 8( c), the limited load becomes substantially constant without overshooting. The overshooting of the limited load makes the inertial energy of the occupant be hardly efficiently absorbed.

There has been proposed a seat belt retractor capable of preventing the limited load from overshooting at the initial stage of the drawing action of the energy absorbing pin 19. In the seat belt retractor shown in FIGS. 9( a) and 9(b), the energy absorbing pin 19 is formed in a crank shape. That is, the shaft portion 19 a comprises a portion 19 a 2, which projects from the head portion 19 b and penetrates the locking base 16, a portion 19 a 3, which is bent at a right angle from the portion 19 a 2 and extends between the spool 9 and the locking base 16, and a portion 19 a 1 which is bent at a right angle from the portion 19 a 3 and is fitted into the axial hole 9 a of the spool 9.

In the normal state as shown in FIG. 9( c), the energy absorbing pin 19 is assembled to the spool 9 and the locking base 16 by setting a predetermined space S1 between the contact surface 19 b 1 of the head portion 19 b and a bottom surface 16 a 1 of a concavity 16 a that is formed in the locking base 16 for accommodating the head portion 19 b. A predetermined space S2 is set between a curved portion between the portion 19 a 3 and the portion 19 a 1 of the shaft portion 19 a and an opening edge portion 9 b of a drawing-side opening of the axial hole 9 a. In this case, the opening edge portion 9 b is rounded.

This arrangement allow the shaft portion 19 a and the head portion 19 b of the energy absorbing pin 19 not to be subjected to bending load immediately after the spool 9 starts to rotate in the belt withdrawing direction relative to the locking base 16. As the spool 9 rotates a predetermined amount relative to the locking base 16, the head portion 19 b tilts so that the space S1 is gone and the contact surface 19 b 1 of the head portion 19 b comes in contact with the bottom portion 16 a 1 of the concavity 16 a as shown by two dot chain lines in FIG. 9( c). At this point, a limited load by the bending load of the head portion 19 b is generated. In addition, the portion 19 a 1 of the shaft portion 19 a is drawn so that the space S2 is gone and the bent portion between the portion 19 a 3 and the portion 19 a 1 comes in contact with the opening edge portion 9 b as also shown by two dot chain lines in FIG. 9( c). At this point, a limited load by the drawing and bending load of the shaft portion 19 a is generated.

Therefore, in the initial stage of the EA action, energy is not absorbed by the energy absorbing pin 19, thereby preventing the overshooting of the limited load as shown by solid line in FIG. 7( a).

However, it is desirable not only to form the energy absorbing pin 19 for a seat belt retractor into a specialized shape or the crank shape but also to control the predetermined spaces S1 and S2 with a high degree of accuracy. Troublesome placement of the energy absorbing pin 19 relative to the other components can cause difficulty obtaining stable limited load. In addition, these problems also cause problems of poor productivity and high cost.

As shown in FIGS. 8( b) and 8(c), as the head portion 19 b of the pin tilts, the end of the head portion 19 b opposite of the bottom portion 16 a 1 of the concavity 16 a moves away from the bottom portion 16 a 1. To accommodate the head portion 19 b so the head portion 19 b does not protrude from the concavity 16 a when it is tilted, the concavity 16 a is configured to be relatively deep in the axial direction of the locking base 16 (e.g., the rightward direction in FIGS. 8( a) through 8(c)). However, deepening the concavity in turn forces other retractor components such as the lock gear 17 of the lock mechanism 11 and an inertia body of a webbing sensor to also be shifted outward in the axial direction. As a result, the size in the axial direction of the spool 9 of the seat belt retractor 3 is increased.

It has been the trend in recent years to widen the space of the vehicle cabin of automobiles without increasing the size of the entire automobile. Accordingly, installation spaces for vehicle components disposed within the vehicle cabin have been further limited. Therefore, it is desired to make the seat belt retractor 3 disposed within the vehicle cabin to be as small as possible. However, as the size of the seat belt retractor 3 is increased as described above, a larger installation space for the seat belt retractor 3 is needed.

According to an exemplary embodiment a seat belt apparatus includes at least: a seat belt retractor for winding up a seat belt; a tongue slidably supported by the seat belt withdrawn from the seat belt retractor; and a buckle to which the tongue can be detachably latched. In the event of an emergency, the seat belt is prevented from being withdrawn by the seat belt retractor so that the seat belt apparatus restrains an occupant.

According to an exemplary embodiment, a seat belt retractor comprising a spool for winding up a seat belt; and a locking mechanism having a locking member that rotates together with the spool in the normal state, but is prevented from rotating in a belt withdrawing direction in the event of an emergency, generating a rotational difference relative to the spool. The rotation of the spool is transmitted to the locking member via the torsion bar. The spool further comprises an energy absorbing pin that is disposed on the spool and the locking member to limit the load applied to the seat belt when the rotational difference is generated between the spool and the locking member.

The energy absorbing pin has a shaft portion that is fitted in a hole of the spool and a head portion that is in contact with the locking member. The head portion comprises a curved contact surface to be in contact with the locking member. The curved surface may be formed into a spherical shape. The head portion is formed into a rod-like shape, and the curved contact surface of the head portion is formed to have an arc or elliptical arc cross section in a direction perpendicular to the longitudinal direction of the head portion. The head portion is in contact with the locking member such that the longitudinal direction of the head portion extends in a radial direction or substantially radial direction of the locking member.

The curved contact surface of the head portion of the energy absorbing pin allows the head portion to relatively easily rotate at the initial stage of the drawing action of the energy absorbing pin so that the head portion and the portion of the shaft portion adjacent to the head portion are hardly bent into a crank shape like the conventional case in which the contact surface is flat. This prevents the limited load from rapidly increasing and thus effectively prevents the limited load from overshooting at the initial stage of the EA action.

Further, since the contact surface of the head portion of the energy absorbing pin is formed to be a curved surface, the energy absorbing pin has a simple structure and can be manufactured easily. The energy absorbing pin may be formed as a linear member and may be manufactured more easily and inexpensively than as a crank shape. Since the energy absorbing pin has a simple structure and it is not necessary to set the predetermined spaces with a high degree of accuracy like the seat belt retractor described above. The energy absorbing pin can be easily assembled to the spool and the locking base and stable limited load can be obtained. This can achieve improved productivity of the seat belt retractor and easily achieve production of inexpensive seat belt retractors.

The curved contact surface allows the head portion to remain in the concavity and not stick out in the axial direction of the locking base (the axial direction of the spool) even while tilted. This allows the locking base to be formed with a shallower concavity and a shorter length in the axial direction. This arrangement allows the seat belt retractor to have a smaller size, thus increasing the vehicle cabin space of the vehicle.

Hereinafter, best modes for carrying out the present invention will be described with reference to the attached drawings.

Referring in general to FIGS. 1-4( a), an energy absorbing pin 19 for a seat belt retractor is shown assembled with a locking base 16 and the spool 9. FIG. 1 is an illustration schematically showing a part of a seat belt retractor. In the following description of the embodiment, the same components as those in the aforementioned embodiment one are marked with the same numerals so that detailed description thereof will be omitted.

As shown in FIG. 1, according to one exemplary embodiment, an energy absorbing pin 19 penetrates a locking base 16 and a portion 19 a 1 of a shaft portion 19 a is fitted in an axial hole 9 a of a spool 9 similarly to the aforementioned example shown in FIGS. 6( a)-6(c). As shown in FIG. 2( a), in the energy absorbing pin 19 of this embodiment, the shaft portion 19 a is a linear member and projects orthogonally from a head portion 19 b. The head portion 19 b is formed to have a rectangular rod-like shape as seen from a side and has a curved contact surface 19 b 1 is an arc surface or an elliptical arc surface. In this case, the rectangular head portion 19 b has a flat surface on the side opposite to the contact surface 19 b 1.

As shown in FIG. 3, the locking base 16 includes a concavity 16 a with an edge 16 b that extends substantially radially (in a direction substantially perpendicular to the rotational direction of the locking base 16) on the α side in the belt withdrawing direction. A linear side edge 19 b 2 of the head portion 19 b of the energy absorbing pin 19 on the a side in the belt withdrawing direction is in plane contact with the radial edge 16 b. As shown in FIG. 1 and FIG. 4( a), the curved contact surface 19 b 1 is partially in contact with the bottom surface 16 a 1 of the concavity 16 a of the locking base 16. It should be noted that the edge 16 b of the concavity 16 a of the locking base 16 may linearly extend in a radial direction of the locking base 16 (in a direction perpendicular to the rotational direction of the locking base 16).

As the spool 9 rotates in the belt withdrawing direction relative to the locking base 16 in the event of an emergency from the normal state shown in FIG. 4( a), the energy absorbing pin 19 is drawn out. As the pin 19 is drawn out, the head portion 19 b is subjected to bending force in the rotational direction of the locking base 16 about an axis in the radial direction of the locking base 16. Since the contact surface 19 b 1 of the energy absorbing pin 19 is a curved surface, the head portion 19 b easy tilts about an axis in the radial direction of the locking base 16 as shown in FIG. 4( b). Tilting on the curved contact surface 19 b 1 does not rapidly increase the limited load at the initial stage of the drawing action of the energy absorbing pin 19, thereby preventing the limited load at the initial stage of the EA action from overshooting. Therefore, as shown in FIG. 7( a), it is possible to obtain substantially constant limited load from the initial stage of the EA action.

As shown in FIG. 4( b), when the head portion 19 b is tilted, the face of the head portion 19 b opposite of the curved contact surface 19 b 1 is not spaced as far away from the bottom surface 16 a 1 of the concavity 16 a as compared to a head portion 19 b with a flat contact surface 19 b 1 (shown in dashed lines). Therefore, the head portion 19 b does not protrude out in the axial direction of the locking base 16 (the axial direction of the spool 9) when the head portion 19 b tilts. This arrangement allows the length of the locking base 16 in the axial direction to be shorter, as shown by solid lines in FIG. 4( b), than that of the locking base 16 in case of using the energy absorbing pin 19 having the flat contact surface 19 b 1 as shown by dashed lines in FIG. 4( b).

According to an exemplary embodiment, the head portion 19 b of the energy absorbing pin 19 is allowed to relatively easily rotate on the curved contact surface 19 b 1 at the initial stage of the drawing action of the energy absorbing pin 19 so that the head portion 19 b and the portion 19 a 2 of the shaft portion 19 a adjacent to the head portion 19 b are hardly bent into a crank shape like the situation in which the contact surface 19 b 1 is flat. This prevents the limited load from rapidly increasing and thus effectively prevents the limited load from overshooting at the initial stage of the EA action.

Further, since the contact surface 19 b 1 of the head portion 19 b is just formed to be a curved surface, the energy absorbing pin 19 of this embodiment has a simple structure and can be manufactured easily. In addition, the energy absorbing pin may be simply formed as a linear member rather than a more complex crank shape. Therefore, the energy absorbing pin 19 can further easily and cheaply manufactured. Since the energy absorbing pin 19 has a simple structure and it is not necessary to set the predetermined spaces S1 and S2 with a high degree of accuracy like the seat belt retractor with e crank-shaped energy absorbing pin 19 described above, the energy absorbing pin 19 can be easily assembled with the spool 9 and the locking base 16 and stable limited load can be obtained. This can achieve improved productivity of the seat belt retractor 3 and easily achieve production of inexpensive seat belt retractor 3.

Even when the head portion 19 b of the energy absorbing pin 19 tilts, the head portion 19 b is prevented from sticking out in the axial direction of the locking base 16 (the axial direction of the spool 9), thereby allowing the locking base 16 to be designed with a shorter length in the axial direction. Therefore, a smaller seat belt retractor 3 may be provided, thus increasing the vehicle cabin space of the vehicle.

Other components of the seat belt retractor 3 of this embodiment are the same as those of the seat belt retractor 3 of the example shown in FIG. 6. The other components and operation of the seat belt retractor 3 of the example shown in FIG. 6 are described in, for example, JP-A-2001-58559 will be easily understood by reading this publication. Therefore, the detailed description of these will be omitted.

The seat belt retractor 3 of this embodiment can be employed in any seat belt apparatus 1 as long as the seat belt apparatus 1 employs the seat belt retractor 3, as well as the seat belt apparatus 1 shown in FIG. 5, for example. Accordingly, an occupant of the vehicle can be efficiently restrained by the seat belt apparatus 1 in the event of an emergency.

FIGS. 2( c) through 2(f) are illustrations of energy absorbing pins of other examples according to the embodiment of the present invention, respectively.

An energy absorbing pin 19 of an example shown in FIGS. 2( c) and 2(d) has a head portion 19 b which is composed of a cylindrical member. The cylindrical member is coupled orthogonally to the shaft portion 19 a. That is, the contact surface 19 b 1 of the head portion 19 b is an arc curved surface. An energy absorbing pin 19 of an example shown in FIGS. 2( e) and 2(f) has a head portion 19 b having a circular shape as seen from a side which is coaxial with a shaft portion 19 a. The contact surface 19 b 1 of the head portion 19 b is a spherical curved surface. In case of the contact surface composed of the spherical curved surface, the head portion 19 b is directionless relative to the locking base in the state that the energy absorbing pin 19 is assembled.

The works and effects of the energy absorbing pin 19 of each example shown in FIGS. 2( c) through 2(f) are the same as the works and effects of the energy absorbing pin 19 of the aforementioned example shown in FIGS. 2( a) and 2(b).

Other components and works and effects of the seat belt retractor 3 employing the energy absorbing pin 19 of each of the examples shown in FIGS. 2( c)-2(f) are the same as those of the example shown in FIG. 1 and FIG. 6.

The seat belt retractor according to the present invention is not limited to the aforementioned embodiments and can be applied to any seat belt retractor employing an energy absorbing pin 19 which is disposed between a spool 9 and a locking base 16 to absorb inertial energy of an occupant in the event of an emergency, within a scope of the claims of the present invention.

Japan Priority Application 2007-277604, filed Oct. 25, 2007 including the specification, drawings, claims and abstract, is incorporated herein by reference in its entirety.

Given the disclosure of the present invention, one versed in the art would appreciate that there may be other embodiments and modifications within the scope and spirit of the invention. Accordingly, all modifications attainable by one versed in the art from the present disclosure within the scope and spirit of the present invention are to be included as further embodiments of the present invention. The scope of the present invention is to be defined as set forth in the following claims. 

1. A seat belt retractor comprising: a spool for winding up a seat belt; a locking mechanism having a locking member that rotates together with the spool in the normal state, but is prevented from rotating in a belt withdrawing direction in the event of an emergency, generating a rotational difference relative to the spool; and an energy absorbing pin that is disposed on the spool and the locking member to limit the load applied to the seat belt when the rotational difference is generated between the spool and the locking member, wherein the energy absorbing pin has a shaft portion that is fitted in a hole of the spool and a head portion that is in contact with the locking member, and wherein the head portion comprises a curved contact surface to be in contact with the locking member.
 2. A seat belt retractor as claimed in claim 1, wherein the rotation of the spool is transmitted to the locking member via the torsion bar.
 3. A seat belt retractor as claimed in claim 1, wherein the curved contact surface of the head portion is formed into a spherical shape.
 4. A seat belt retractor as claimed in claim 1, wherein the head portion is formed into a rod-like shape, and the curved contact surface of the head portion is formed to have an arc or elliptical arc cross section in a direction perpendicular to the longitudinal direction of the head portion, and wherein the head portion is in contact with the locking member such that the longitudinal direction of the head portion extends in a radial direction or substantially radial direction of the locking member.
 5. A seat belt apparatus comprising: a seat belt retractor for winding up a seat belt; a tongue slidably supported by the seat belt withdrawn from the seat belt retractor; and a buckle to which the tongue can be detachably latched, wherein in the event of an emergency, the seat belt is prevented from being withdrawn by the seat belt retractor so that the seat belt apparatus restrains an occupant; wherein the seat belt retractor comprises a spool for winding up a seat belt and a locking mechanism having a locking member that rotates together with the spool in the normal state, but is prevented from rotating in a belt withdrawing direction in the event of an emergency, generating a rotational difference relative to the spool, and an energy absorbing pin that is disposed on the spool and the locking member to limit the load applied to the seat belt when the rotational difference is generated between the spool and the locking member; wherein the energy absorbing pin has a shaft portion that is fitted in a hole of the spool and a head portion that is in contact with the locking member, and wherein the head portion comprises a curved contact surface positioned to be in contact with the locking member.
 6. The apparatus of claim 5, wherein the curved contact surface of the head portion is formed into a spherical shape.
 7. The apparatus of claim 5, wherein the head portion is formed into a rod-like shape, and the curved contact surface of the head portion is formed to have an arc or elliptical arc cross section in a direction perpendicular to the longitudinal direction of the head portion, and wherein the head portion is in contact with the locking member such that the longitudinal direction of the head portion extends in a radial direction or substantially radial direction of the locking member.
 8. A seat belt apparatus comprising: a tongue connected to a seat belt, wherein the tongue is configured to be releasably connected to a buckle; and wherein in the event of a condition involving the vehicle, the retractor prevents the seat belt from being withdrawn; a seat belt retractor for winding up the seat belt, wherein the retractor includes a spool for winding up a seat belt and a locking member that normally rotates together with the spool; wherein the locking member is prevented from rotating in a belt withdrawing direction in the event of an emergency, thereby generating a rotational difference between the locking member and the spool; wherein the retractor includes an energy absorbing pin configured to limit the load applied to the seat belt when the rotational difference is generated between the spool and the locking member, the pin including a shaft portion fitted in a hole of the spool and a head portion in contact with the locking member, and wherein the head portion includes a curved contact surface positioned to be in contact with the locking member. 